1. Field of the Invention
This invention relates to new synthetic, finely divided, water-in-soluble layered silicates having a smectite-like crystal phase. The layered silicates are distinguished from known natural and synthetic smectite-based layered silicates, in particular montmorillonite, hectorite and saponite for example, by a distinctly reduced swelling power in aqueous suspension. The invention also relates to processes for producing these smectite-like layered silicates and to their use as environmentally neutral constituents of detergents and cleaning preparations, more especially to their use as a builder constituent of low-phosphate and phosphate-free laundry detergents containing synthetic surfactants.
2. Description of Related Art
The replacement of phosphate builders, particularly sodium tripolyphosphate (STP), in detergents and cleaning preparations containing synthetic surfactants is described, for example, in DE-AS No. 24 12 837. In practice, zeolite NaA has proven to be an entirely satisfactory replacement for STP, particularly for laundry detergents. In this connection, it also was proposed to use synthetic, crystalline, non-swelling aluminosilicates of the zeolite type in admixture with water-insoluble, swellable magnesium and/or aluminum silicates of the bentonite, montmorillonate, hectorite or saponite type as detergent builders. Thus, U.S. Pat. No. 4,438,012 describes pumpable aqueous suspensions of improved stability, for example, of zeolite A, which contain as their constituent highly swellable smectite-based layered silicates of the type mentioned above.
Numerous proposals both in the literature and in practice are concerned with the partial or complete replacement of the STP builder in laundry detergents by builder systems based on synthetic, crystalline, non-swelling zeolites, particularly based on zeolite NaA. The STP builder is undesirable for ecological reasons, although as recently as a decade ago, it was still being used as virtually the only detergent builder. Successful use of the synthetic zeolite has included so-called co-builders in small quantities together with the insoluble crystalline zeolite as the principal builder constituent. These co-builders generally are soluble components capable of complexing alkaline earth metal ions from stains on the laundry. Hence, both primary and secondary detergency are distinctly improved over detergent mixtures free from such co-builders. Primary detergency relates to the degree of whitening obtained by washing soiled test materials one or more times under standard conditions. Secondary detergency relates inter alia to the degree of redeposition and incrustation on the textile fibers after repeated washing under standard conditions, for example, after 25 or after 50 washes with a particular detergent.
Today, the use of, for example, nitrilotriacetic acid salts (NTA) and/or polyphosphonic acid salts, such as corresponding salts of hydroxyethane diphosphonic acid (HEDP), as a co-builder constituent is standard practice for STP-free detergents based on synthetic surfactants and zeolite A as the main builder constituent. Although these co-builders are used in only small quantities in the detergents by virtue of their high effectiveness (generally only a few weight percent), it would now appear desirable--in the light of more stringent water pollution control requirements, to replace completely or at least partially even these small amounts of co-builders in favor of other components of comparable effect. Co-builders of this latter type known both in practice and in the literature are, for example, organic macromolecular polymer compounds containing carboxyl and/or hydroxyl groups of the type described, for example, in U.S. Pat. No. 4,438,012.
The use of highly swellable, finely divided layered silicates or clays in detergents has been known for many decades. Natural and/or synthetic crystalline smectites having a highly swellable layered structure have been proposed as a constituent of laundry detergents in various connections. Natural bentonite for example has been repeatedly proposed as a detergent or detergent substitute. Today, corresponding synthetic or semi-synthetic, water-insoluble, finely divided layered silicates of smectite structure and, more particularly, corresponding hectorites, saponites and montmorillonites are well-known commercial products for numerous applications. A crucial factor here is always the high swellability which relates to the ability of this class of layered silicates to incorporate water and/or organic, cationic compounds into the crystal lattice with widening of the layer intervals.
The use of materials such as these in connection with laundry detergents relates in particular to two principles. It is known that swellable layered silicates and, in particular, montmorillonite, hectorite and saponite in the sodium form are deposited in thin layers on textile fibers and, hence, affect the softness and feel of the washed fabrics. With this in mind, attempts have been made to combine the washing and softening of fabrics into a single operation, and this recently has been addressed again, for example in DE-PS No. 23 34 899.
According to more recent proposals, the known use of strongly swelling clays having a smectite-like layered structure, particularly bentonite, in conjunction with finely crystalline synthetic zeolites as builders in laundry detergents based on synthetic surfactants is based on another consideration. The crystalline alumosilicates are intended to disintegrate very quickly in the wash water to form a suspension of ultrafine primary particles. However, if the detergents and/or builder components have been produced under conditions which otherwise would lead to agglomeration of the fine zeolite particles into non-readily disintegrating agglomerates, by also incorporating the highly swellable smectite clays in the zeolite material by thorough mixing, the desired disintegrating effect is nonetheless produced in the wash liquor and rapid disintegration of the insoluble fractions of the detergent mixture into a very finely divided form occurs.
An object of the present invention is to provide environmentally neutral constituents for builder systems based on insoluble, very finely divided, synthetic, crystalline zeolite materials and, more particularly, on zeolite NaA for the complete or partial replacement of STP. The present builder system renders the use of co-builders (particularly NTA and/or polyphosphonic acid salts) largely superfluous while, at the same time, ensuring good primary and/or secondary detergency of the detergent mixtures in line with today's stringent requirements.